A high-toughness polyimide composite material, its preparation method, and its application in aviation cables.

Abstract

This invention relates to the field of polymer materials technology, specifically providing a high-toughness polyimide composite material, its preparation method, and its application in aerospace cables. The composite material consists of a polyimide prepolymer, a flexible diamine modifier, an organosilicon elastomer, a hydroxyl-termining agent, surface-modified carbon nanotubes, layered silicate sheets, a dispersant stabilizer, and a highly polar organic solvent. By introducing a dual mechanism of flexible segments and nano-reinforcement, structural densification and interface stabilization are achieved under multi-stage heat treatment and interface activation conditions. The resulting material exhibits excellent elongation at break, impact strength, and thermal stability, making it suitable for the preparation of aerospace cable sheaths and significantly improving the flexibility, crack resistance, and service life of cables under alternating high and low temperature environments.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a high-toughness polyimide composite material, its preparation method, and its application in aviation cables. Background Technology

[0002] Polyimide (PI) is a class of high-performance polymer materials with excellent thermal stability, electrical insulation, mechanical properties, and chemical stability, and is widely used in aerospace, electronics, electrical engineering, and high-temperature insulation. However, conventional polyimides, due to their rigid molecular backbone structure, typically exhibit high brittleness and poor ductility, limiting their application in harsh conditions such as flexible cables and fold-resistant composite layers.

[0003] To improve the toughness and processing performance of polyimide materials, existing technologies often employ molecular structure modification, blending, or composite reinforcement. For example, introducing flexible diamines or linear segments can improve the material's flexibility to some extent, but often at the expense of thermal properties; adding inorganic nanomaterials such as carbon nanotubes and montmorillonite can improve mechanical strength, but issues with dispersion stability and interfacial compatibility remain; the introduction of organosilicon elastomers can impart flexibility and weather resistance to the material, but it is difficult to achieve stable chemical bonding with the polyimide backbone, leading to easy degradation of interfacial properties.

[0004] In addition, some existing heat treatment processes for composite materials are too simplified, failing to fully complete the imidization and crosslinking reactions, and failing to effectively control the interfacial compatibility between the composite material and the application substrate (such as aviation cables), resulting in overall performance that is difficult to meet the needs of actual engineering applications.

[0005] Therefore, there is an urgent need to provide a novel polyimide composite material with high toughness, high thermal stability, and good interfacial bonding, along with a controllable preparation process, to meet its stringent application requirements in scenarios such as high-performance cable sheath materials. Summary of the Invention

[0006] To address the issues of poor toughness, weak interfacial bonding, and insufficient processing stability in existing polyimide materials, this invention provides a high-toughness polyimide composite material, its preparation method, and its application in aviation cables. Through multi-component synergistic design and graded reaction control, it achieves a comprehensive improvement in mechanical properties, thermal stability, and interfacial compatibility, making it suitable for aviation cable systems with high requirements for insulation sheath performance.

[0007] To achieve the above objectives, the present invention proposes the following technical solution:

[0008] On the one hand, a high-toughness polyimide composite material is proposed, comprising the following components by mass percentage: 30%–50% polyimide prepolymer, 10%–20% flexible diamine modifier, 5%–12% hydroxyl end-capping agent, 1%–8% surface-modified carbon nanotubes, 1%–5% silicone elastomer, 0.1%–2% layered silicate sheet, 0.1%–1% dispersant stabilizer, and the remainder being a highly polar organic solvent;

[0009] The polyimide prepolymer is prepared by polycondensation of dianhydride monomer and aromatic diamine in solution. The flexible diamine modifier contains ether bonds or aliphatic segments. The surface-modified carbon nanotubes are subjected to amylation or carboxylation treatment to introduce polar functional groups on their surface, thereby enhancing their interfacial bonding with the polyimide matrix in the dispersed state. The layered silicate sheet is surface-modified with a trimethoxysilane coupling agent.

[0010] Further, the material preferably comprises the following components in weight percentage: 40%–48% polyimide prepolymer, 15%–18% flexible diamine modifier, 8%–10% hydroxyl end-capping agent, 3%–6% surface-modified carbon nanotubes, 3%–4% silicone elastomer, 0.3%–1% layered silicate sheet, 0.2%–0.5% dispersion stabilizer, and the remainder being highly polar organic solvents.

[0011] Furthermore, the polyimide prepolymer is prepared by reacting pyromellitic dianhydride with 4,4'-diaminodiphenyl ether. The resulting polyimide prepolymer has a rigid linear molecular chain structure and a glass transition temperature higher than 250°C.

[0012] Furthermore, the flexible diamine modifier is polyoxypropylene diamine, with a molecular weight controlled between 400 and 1500 Daltons, and contains two main chain terminal amine groups.

[0013] Furthermore, the organosilicon elastomer is a room-temperature curing elastomer with a polydimethylsiloxane backbone structure, containing terminal amino or carboxyl groups in its molecule, which undergo a chemical bonding reaction with the polyimide prepolymer.

[0014] On the other hand, the present invention also provides a method for preparing the high-toughness polyimide composite material, comprising the following steps:

[0015] S1. In a highly polar organic solvent, dianhydride monomer and aromatic diamine are mixed and reacted in a molar ratio of 1:1 and stirred at room temperature to 35°C for 8 hours to generate a polyimide prepolymer solution.

[0016] S2. Add the flexible diamine modifier, organosilicon elastomer, and dispersant stabilizer to the above solution and continue stirring for 2 hours.

[0017] S3. Under ultrasonic assistance, surface-modified carbon nanotubes modified with amino or carboxyl groups and layered silicate sheets are added to the system and dispersed for 30 minutes.

[0018] S4. Add hydroxyl-capping agent to terminate the reaction and obtain precursor resin solution;

[0019] S5. After casting or spin-coating the resin solution into a film, perform multi-stage heat treatment at 80℃, 150℃, 250℃ and 300℃ in sequence, holding at each temperature for 1 hour to complete the imidization and partial crosslinking reaction.

[0020] Furthermore, in step S3, a probe-type ultrasonic dispersion device is used with a power controlled at 300 watts, and three ultrasonic treatments are performed, each lasting 10 minutes with a 5-minute interval in between.

[0021] Furthermore, the following steps are included after step S5:

[0022] S61. The surface of the composite membrane is activated by plasma or ultraviolet irradiation.

[0023] S62. A siloxane coating with a thickness of 1 to 5 micrometers is applied by sol-gel assisted coating. During the thermosetting process, the coating forms a dense three-dimensional cross-linked siloxane network structure, forming multi-point non-covalent interactions at the interface, thereby improving the adhesion between the composite film and the fluoropolymer insulating layer.

[0024] The present invention also proposes an application of the high-toughness polyimide composite material in aviation cables. Specifically, the composite material is used in the preparation of aviation cable sheaths, with the sheath thickness controlled between 20 and 150 micrometers. It is attached to the outside of the cable core layer by hot extrusion or lamination process to improve the flexibility, wear resistance and crack resistance of the cable in high and low temperature alternating environments.

[0025] Furthermore, the aviation cable structure includes: an inner layer of copper conductor, a middle layer of fluorinated ethylene propylene copolymer or polytetrafluoroethylene insulation layer, and an outer layer of the high-toughness polyimide composite material sheath.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Flexible chain segment synergistic regulation: In view of the problems of excessive rigidity and poor fracture elongation of traditional polyimide materials, this invention introduces a dual flexible chain segment of flexible diamine and organosilicon elastomer to achieve flexible regulation of the molecular main chain. Under the premise of keeping Tg above 250℃, the elongation at break and impact resistance are improved, and its ability to adapt to bending and dynamic load is significantly enhanced.

[0028] (2) Interface reinforcement design: By introducing carbon nanotubes modified with polar functional groups and layered silicate sheets, a dispersed and stable reinforcement network is constructed in synergy, avoiding the aggregation and peeling of nanofillers, effectively improving the energy storage modulus and interface strength, and forming a stable stress transfer structure.

[0029] (3) Dispersion and heat treatment optimization: Ultrasonic-assisted treatment is used to enhance the uniformity of nano-components, and hydroxyl end-capping and multi-stage heat treatment process of 80-300℃ are used to fully imidize the polyimide structure and introduce cross-linking scaffolds to form a composite film with dense structure and high pyrolysis temperature, which significantly improves heat resistance.

[0030] (4) Strong application adaptability: The post-processing constructs a silicon-oxygen network coating, which effectively enhances the adhesion of composite materials to cable insulation materials such as fluoropolymers, ensuring that they maintain structural integrity and stable performance in complex service environments. Attached Figure Description

[0031] Figure 1 This is a flowchart of the preparation method of the present invention;

[0032] Figure 2 This is a comparison chart of the mechanical properties of the present invention;

[0033] Figure 3 This is a comparison chart of the thermal performance of the present invention;

[0034] Figure 4 This is a schematic diagram of the microstructure of the polyimide composite material of the present invention. Detailed Implementation

[0035] To more clearly illustrate the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0038] Raw material composition (by mass percentage):

[0039] Polyimide prepolymer: 45%, flexible diamine modifier: 16%, hydroxyl end-capping agent: 9%, surface-modified carbon nanotubes: 5%, silicone elastomer: 3.5%, layered silicate sheet: 0.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (N-methylpyrrolidone, NMP): equilibrated to 100%.

[0040] Preparation method:

[0041] S1. Preparation of polyimide prepolymer solution: In a dry three-necked flask, add an appropriate amount of NMP as solvent. While stirring, add pyromellitic dianhydride and 4,4'-diaminodiphenyl ether sequentially at a molar ratio of 1:1. Control the reaction temperature between room temperature and 35°C and continue stirring for 8 hours to form a viscous and homogeneous polyimide prepolymer solution. This prepolymer has a rigid linear molecular backbone with a glass transition temperature higher than 250°C, exhibiting good thermal stability.

[0042] S2. Introduction of modifiers and additives: Polypropylene diamine (molecular weight approximately 1000, Dalton grade, containing two terminal amino groups) is added to the above prepolymer solution as a flexible diamine modifier. At the same time, room temperature curing polydimethylsiloxane elastomer (containing amino groups at the end) and dispersant stabilizer (polyvinylpyrrolidone PVP) are added. The reaction is continued for 2 hours under stirring to make the modifier and main chain uniformly mixed and partially pre-reacted, thereby improving the flexibility and interfacial stability of the system.

[0043] S3. Nanomaterial Dispersion Treatment: Weigh out the amination-modified carbon nanotubes and the trimethoxysilane coupling agent-modified layered silicate sheets, and add them to the aforementioned mixed solution. Use a probe-type ultrasonic dispersion device for ultrasonic treatment, setting the power to 300W, ultrasonicating 3 times, 10 minutes each time, with a 5-minute interval, to ensure uniform dispersion of the nanomaterials and prevent agglomeration, thereby enhancing their interfacial interaction and mechanical strengthening effect in the matrix.

[0044] S4. Termination of the reaction and preparation of the precursor resin: A hydroxyl-termining agent (p-hydroxybenzyl alcohol) is added dropwise to the above solution to terminate the molecular chain growth reaction and block the terminal active sites, thereby controlling the molecular weight distribution and crosslinking density of the prepolymer. After the reaction is complete, a homogeneous precursor resin solution is obtained.

[0045] S5. Film Formation and Heat Treatment Imidization: The precursor resin solution is spread onto a clean glass or metal substrate using a casting method, controlling the initial film thickness to be 80 micrometers. Subsequently, heat treatment is performed sequentially:

[0046] Keep at 80℃ for 1 hour to remove residual solvent;

[0047] Initiation of imine ring formation occurs when the temperature is maintained at 150℃ for 1 hour.

[0048] Incubate at 250℃ for 1 hour to promote complete imidization of the main chain;

[0049] Finally, the mixture was kept at 300℃ for 1 hour to achieve structural densification and partial cross-linking reaction.

[0050] The aforementioned multi-stage heat treatment enables the polyimide structure to form a complete imide ring, thereby improving the material's thermal stability and resistance to media.

[0051] The material surface is further activated by surface energy level treatment, which involves irradiating it with plasma for 10 minutes to introduce polar groups and improve surface activity. Subsequently, a siloxane coating of about 3 micrometers thick is applied to the surface using sol-gel technology and then thermo-cured at 180°C for 1 hour to form a dense three-dimensional cross-linked structure, thereby improving the adhesion of the composite material to other polymer insulating layers.

[0052] Example 2

[0053] This embodiment provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0054] Raw material composition (by mass percentage): polyimide prepolymer: 40%, flexible diamine modifier: 15%, hydroxyl end-capping agent: 8%, surface-modified carbon nanotubes: 3%, silicone elastomer: 3%, layered silicate sheet: 0.3%, dispersant stabilizer: 0.2%, highly polar organic solvent (N-methylpyrrolidone, NMP): equilibrated to 100%.

[0055] Preparation method:

[0056] S1. Preparation of polyimide prepolymer solution: In a dry three-necked flask, add an appropriate amount of NMP as solvent. While stirring, add pyromellitic dianhydride and 4,4'-diaminodiphenyl ether sequentially at a molar ratio of 1:1. Control the reaction temperature between room temperature and 35°C and continue stirring for 8 hours to form a viscous and homogeneous polyimide prepolymer solution. This prepolymer has a rigid linear molecular backbone with a glass transition temperature higher than 250°C, exhibiting good thermal stability.

[0057] S2. Introduction of modifiers and additives: Polypropylene diamine (molecular weight approximately 1000, Dalton grade, containing two terminal amino groups) is added to the above prepolymer solution as a flexible diamine modifier. At the same time, room temperature curing polydimethylsiloxane elastomer (containing amino groups at the end) and dispersant stabilizer (polyvinylpyrrolidone PVP) are added. The reaction is continued for 2 hours under stirring to make the modifier and main chain uniformly mixed and partially pre-reacted, thereby improving the flexibility and interfacial stability of the system.

[0058] S3. Nanomaterial Dispersion Treatment: Weigh out the amination-modified carbon nanotubes and the trimethoxysilane coupling agent-modified layered silicate sheets, and add them to the aforementioned mixed solution. Use a probe-type ultrasonic dispersion device for ultrasonic treatment, setting the power to 300W, ultrasonicating 3 times, 10 minutes each time, with a 5-minute interval, to ensure uniform dispersion of the nanomaterials and prevent agglomeration, thereby enhancing their interfacial interaction and mechanical strengthening effect in the matrix.

[0059] S4. Termination of the reaction and preparation of the precursor resin: A hydroxyl-termining agent (p-hydroxybenzyl alcohol) is added dropwise to the above solution to terminate the molecular chain growth reaction and block the terminal active sites, thereby controlling the molecular weight distribution and crosslinking density of the prepolymer. After the reaction is complete, a homogeneous precursor resin solution is obtained.

[0060] S5. Film Formation and Heat Treatment Imidization: The precursor resin solution is spread onto a clean glass or metal substrate using a casting method, controlling the initial film thickness to be 80 micrometers. Subsequently, heat treatment is performed sequentially: holding at 80°C for 1 hour to remove residual solvent; holding at 150°C for 1 hour to initiate imide ring formation; holding at 250°C for 1 hour to promote complete imidization of the main chain; and finally holding at 300°C for 1 hour to achieve structural densification and partial cross-linking. This multi-stage heat treatment results in the formation of complete imide rings in the polyimide structure, improving the material's thermal stability and resistance to various media.

[0061] Example 3

[0062] This embodiment provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0063] Raw material composition (by mass percentage): polyimide prepolymer: 48%, flexible diamine modifier: 18%, hydroxyl end-capping agent: 10%, surface-modified carbon nanotubes: 6%, silicone elastomer: 4%, layered silicate sheet: 1%, dispersant stabilizer: 0.5%, highly polar organic solvent (N-methylpyrrolidone, NMP): equilibrated to 100%.

[0064] Preparation method:

[0065] S1. Preparation of polyimide prepolymer solution: In a dry three-necked flask, add an appropriate amount of NMP as solvent. While stirring, add pyromellitic dianhydride and 4,4'-diaminodiphenyl ether sequentially at a molar ratio of 1:1. Control the reaction temperature between room temperature and 35°C and continue stirring for 8 hours to form a viscous and homogeneous polyimide prepolymer solution. This prepolymer has a rigid linear molecular backbone with a glass transition temperature higher than 250°C, exhibiting good thermal stability.

[0066] S2. Introduction of modifiers and additives: Polypropylene diamine (molecular weight approximately 1000, Dalton grade, containing two terminal amino groups) is added to the above prepolymer solution as a flexible diamine modifier. At the same time, room temperature curing polydimethylsiloxane elastomer (containing amino groups at the end) and dispersant stabilizer (polyvinylpyrrolidone PVP) are added. The reaction is continued for 2 hours under stirring to make the modifier and main chain uniformly mixed and partially pre-reacted, thereby improving the flexibility and interfacial stability of the system.

[0067] S3. Nanomaterial Dispersion Treatment: Weigh out the amination-modified carbon nanotubes and the trimethoxysilane coupling agent-modified layered silicate sheets, and add them to the aforementioned mixed solution. Use a probe-type ultrasonic dispersion device for ultrasonic treatment, setting the power to 300W, ultrasonicating 3 times, 10 minutes each time, with a 5-minute interval, to ensure uniform dispersion of the nanomaterials and prevent agglomeration, thereby enhancing their interfacial interaction and mechanical strengthening effect in the matrix.

[0068] S4. Termination of the reaction and preparation of the precursor resin: A hydroxyl-termining agent (p-hydroxybenzyl alcohol) is added dropwise to the above solution to terminate the molecular chain growth reaction and block the terminal active sites, thereby controlling the molecular weight distribution and crosslinking density of the prepolymer. After the reaction is complete, a homogeneous precursor resin solution is obtained.

[0069] S5. Film Formation and Heat Treatment Imidization: The precursor resin solution is spread onto a clean glass or metal substrate using a casting method, controlling the initial film thickness to be 80 micrometers. Subsequently, heat treatment is performed sequentially: holding at 80°C for 1 hour to remove residual solvent; holding at 150°C for 1 hour to initiate imide ring formation; holding at 250°C for 1 hour to promote complete imidization of the main chain; and finally holding at 300°C for 1 hour to achieve structural densification and partial cross-linking. This multi-stage heat treatment results in the formation of complete imide rings in the polyimide structure, improving the material's thermal stability and resistance to various media.

[0070] Comparative Example 1

[0071] This comparative example provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0072] Raw material composition (by mass percentage): polyimide prepolymer: 59%, hydroxyl end-capping agent: 9%, surface-modified carbon nanotubes: 5%, layered silicate sheets: 0.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (NMP): equilibrated to 100%.

[0073] Preparation method: In step S2, no flexible diamine modifier or organosilicon elastomer is added; the remaining steps are the same as in Example 1.

[0074] Comparative Example 2

[0075] This comparative example provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0076] Raw material composition (by mass percentage): polyimide prepolymer: 45%, flexible diamine modifier: 16%, hydroxyl end-capping agent: 9%, silicone elastomer: 3.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (NMP): equilibrated to 100%.

[0077] Preparation method: In step S3, no surface-modified carbon nanotubes and layered silicate sheets are added, and no ultrasonic dispersion is performed. The remaining steps are the same as in Example 1.

[0078] Comparative Example 3

[0079] This comparative example provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0080] Raw material composition (by mass percentage): polyimide prepolymer: 60%, flexible diamine modifier: 8%, hydroxyl end-capping agent: 10%, surface-modified carbon nanotubes: 5%, silicone elastomer: 2%, layered silicate sheet: 0.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (NMP): equilibrated to 100%.

[0081] Preparation method: All steps are the same as in Example 1.

[0082] Comparative Example 4

[0083] This comparative example provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0084] Raw material composition (by mass percentage): polyimide prepolymer: 45%, flexible diamine modifier (hexamethylenediamine): 16%, hydroxyl end-capping agent: 9%, surface-modified carbon nanotubes: 5%, silicone elastomer: 3.5%, layered silicate sheet: 0.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (NMP): equilibrated to 100%.

[0085] Preparation method: In step S2, the flexible diamine modifier is replaced with a straight-chain aliphatic diamine, and the remaining steps are the same as in Example 1.

[0086] Comparative Example 5

[0087] This comparative example provides a high-toughness polyimide composite material and its preparation method. The component ratios and specific steps are as follows:

[0088] Raw material composition (by mass percentage): polyimide prepolymer: 45%, flexible diamine modifier: 16%, hydroxyl end-capping agent: 9%, surface-modified carbon nanotubes: 5%, silicone elastomer: 3.5%, layered silicate sheet: 0.5%, dispersant stabilizer: 0.3%, highly polar organic solvent (NMP): equilibrated to 100%.

[0089] Preparation method: In step S3, ultrasonic dispersion is not performed; instead, magnetic stirring is used for 30 minutes. In step S5, the stepwise heat treatment is cancelled and replaced with a single heat treatment at 250°C for 2 hours. The remaining steps are the same as in Example 1.

[0090] To verify the performance improvement effect of the high-toughness polyimide composite material proposed in this invention and the significant synergistic effect of components and processes, systematic tests and comparisons were conducted on the samples prepared in Examples 1-3 and Comparative Examples 1-5.

[0091] All tested samples were prepared according to the component ratio and preparation process provided by the present invention. Example 1 adopted the optimal ratio and complete process, while the comparative sample made key adjustments in the component ratio or process to simulate the non-optimal conditions commonly found in existing solutions.

[0092] Performance test items and test methods:

[0093] (1) Tensile strength; using a universal testing machine; operating conditions: tensile rate 10 mm / min, room temperature environment;

[0094] (2) Elongation at break; using a universal testing machine; execution conditions: obtained simultaneously with tensile strength;

[0095] (3) Impact strength; simply supported beam impact test; operating conditions: tensile rate using standard specimens, room temperature environment;

[0096] (4) Thermogravimetric analysis (TGA, ASTM E1131); Operating conditions: heating rate 10℃ / min, nitrogen atmosphere;

[0097] (5) Glass transition temperature (Tg); Dynamic mechanical analyzer DMA (ASTM D4065); Operating conditions: heating rate 3℃ / min, frequency 1Hz;

[0098] (6) Storage modulus E′; Dynamic mechanical analyzer DMA (ASTM D4065); Operating conditions: room temperature, tensile mode;

[0099] (7) Loss factor tanδ; Dynamic mechanical analyzer DMA (ASTM D4065); characterizes the degree of coordination of chain segment motion.

[0100] All test samples were prepared using materials from the same batch, with a sample size of 5 pieces. The average value was taken as the representative data, with an error range within ±5%. The test results are shown in Tables 1 and 3.

[0101] Table 1: Mechanical property test results (mean ± standard deviation)

[0102]

[0103] Table 2: Thermal Performance and Dynamic Performance Data of DMA

[0104] serial number Thermogravimetric initiation temperature (°C) Tg(DMA,℃) Energy storage modulus E′ (MPa) tanδ peak value Example 1 526±3 282 2350 0.16 Example 2 522±2 273 2130 0.19 Example 3 525±3 278 2270 0.17 Comparative Example 1 522±2 263 1850 0.23 Comparative Example 2 510±4 258 1910 0.21 Comparative Example 3 540±5 285 2480 0.13 Comparative Example 4 525±3 265 1950 0.22 Comparative Example 5 498±6 254 1780 0.26

[0105] The results in the table show that Example 1 exhibits the best performance across all performance indicators, with a tensile strength of 155.2 MPa, an elongation at break of 18.5%, and an impact strength of 9.3 kJ / m. 2 The temperature Tg was 282℃, the storage modulus E′ reached 2350MPa, and the peak tanδ was only 0.16, indicating that the molecular chain segments of this sample had strong cooperative motion and a uniform and dense overall structure. The mechanical and thermal properties of Examples 2 and 3 were slightly lower than those of Example 1, but were still far superior to the comparative examples.

[0106] Comparative Example 1: The elongation at break was only 9.7%, and the peak tanδ increased to 0.23, indicating a significant lack of inter-segment flexibility and increased material brittleness; Comparative Example 2: Both tensile strength and storage modulus E′ decreased, and the impact strength was only 6.0 kJ / m. 2 The results show that the nanofiller plays an irreplaceable supporting role in the reinforcing network. Comparative Example 3: The thermal stability and Tg are slightly higher, but the elongation at break is as low as 6.8%, and the tanδ peak value is low, indicating that the lack of flexibility adjustment leads to the loss of material ductility. Comparative Example 4: The tensile strength decreases to 138.9 MPa, and the tanδ peak value increases to 0.22, showing that the mismatch of flexible structure will significantly weaken molecular synergy. Comparative Example 5: The thermal weight loss onset temperature drops to 498℃, the storage modulus E′ is the lowest, only 1780 MPa, and the tanδ peak value is as high as 0.26, indicating that it is not fully imamidized and the structure is loose.

[0107] The above experimental data fully verify that the component ratio, flexible chain segment introduction mechanism, nano-reinforcement system and multi-stage heat treatment process proposed in this invention have a significant synergistic enhancement effect. The scheme shown in Example 1 is not only the best in various performance aspects, but also has good comprehensive controllability, supporting the creativity and significant practicality of the technical solution of this invention.

[0108] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A high-toughness polyimide composite material, characterized in that, It comprises the following components by weight percentage: 30%–50% polyimide prepolymer, 10%–20% flexible diamine modifier, 5%–12% hydroxyl end-capping agent, 1%–8% surface-modified carbon nanotubes, 1%–5% silicone elastomer, 0.1%–2% layered silicate sheet, 0.1%–1% dispersant stabilizer, and the remainder being highly polar organic solvent; The polyimide prepolymer is prepared by reacting pyromellitic dianhydride with 4,4'-diaminodiphenyl ether at a molar ratio of 1:1; the flexible diamine modifier is polyoxypropylene diamine with a molecular weight controlled between 400 and 1500 Daltons and containing two terminal amino groups in the main chain; the surface-modified carbon nanotubes are subjected to amylation or carboxylation treatment to introduce polar functional groups on their surface to enhance their interfacial bonding with the polyimide matrix in the dispersed state; the layered silicate sheet is surface-modified with a trimethoxysilane coupling agent; the organosilicon elastomer is a room-temperature curing elastomer with a polydimethylsiloxane main chain structure, containing terminal amino or carboxyl groups in its molecule, which undergoes a chemical bonding reaction with the polyimide prepolymer; The high-toughness polyimide composite material is prepared by the following steps: S1. In a highly polar organic solvent, pyromellitic dianhydride and 4,4'-diaminodiphenyl ether are mixed and reacted in a molar ratio of 1:1 and stirred at room temperature to 35°C for 8 hours to generate a polyimide prepolymer solution. S2. Add the flexible diamine modifier, organosilicon elastomer, and dispersant stabilizer to the above solution and continue stirring for 2 hours. S3. Under ultrasonic assistance, surface-modified carbon nanotubes modified with amino or carboxyl groups and layered silicate sheets are added to the system and dispersed for 30 minutes. S4. Add hydroxyl-capping agent to terminate the reaction and obtain precursor resin solution; S5. After casting or spin-coating the resin solution into a film, perform multi-stage heat treatment at 80℃, 150℃, 250℃ and 300℃ in sequence, holding at each temperature for 1 hour to complete the imidization and partial crosslinking reaction.

2. The high-toughness polyimide composite material according to claim 1, characterized in that, The composition includes the following components by weight percentage: 40%–48% polyimide prepolymer, 15%–18% flexible diamine modifier, 8%–10% hydroxyl end-capping agent, 3%–6% surface-modified carbon nanotubes, 3%–4% silicone elastomer, 0.3%–1% layered silicate sheet, 0.2%–0.5% dispersant stabilizer, and the remainder being highly polar organic solvents.

3. The high-toughness polyimide composite material according to claim 1, characterized in that, The resulting polyimide prepolymer has a rigid linear molecular chain structure and a glass transition temperature higher than 250℃.

4. A method for preparing a high-toughness polyimide composite material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. In a highly polar organic solvent, pyromellitic dianhydride and 4,4'-diaminodiphenyl ether are mixed and reacted in a molar ratio of 1:1 and stirred at room temperature to 35°C for 8 hours to generate a polyimide prepolymer solution. S2. Add the flexible diamine modifier, organosilicon elastomer, and dispersant stabilizer to the above solution and continue stirring for 2 hours. S3. Under ultrasonic assistance, surface-modified carbon nanotubes modified with amino or carboxyl groups and layered silicate sheets are added to the system and dispersed for 30 minutes. S4. Add hydroxyl-capping agent to terminate the reaction and obtain precursor resin solution; S5. After casting or spin-coating the resin solution into a film, perform multi-stage heat treatment at 80℃, 150℃, 250℃ and 300℃ in sequence, holding at each temperature for 1 hour to complete the imidization and partial crosslinking reaction.

5. The preparation method according to claim 4, characterized in that, In step S3, a probe-type ultrasonic dispersion device is used with a power controlled at 300 watts, and three ultrasonic treatments are performed, each lasting 10 minutes with a 5-minute interval in between.

6. The preparation method according to claim 4, characterized in that, The following steps are included after step S5: S61. The surface of the composite membrane is activated by plasma or ultraviolet irradiation. S62. A siloxane coating with a thickness of 1 to 5 micrometers is applied by sol-gel assisted coating. During the thermosetting process, the coating forms a dense three-dimensional cross-linked siloxane network structure, forming multi-point non-covalent interactions at the interface, thereby improving the adhesion between the composite film and the fluoropolymer insulating layer.

7. The application of a high-toughness polyimide composite material as described in any one of claims 1 to 3 in aviation cables, characterized in that, The composite material is used in the preparation of aviation cable sheaths, with the sheath thickness controlled between 20 and 150 micrometers. It is attached to the outside of the cable core layer by hot extrusion or lamination process to improve the flexibility, wear resistance and crack resistance of the cable in high and low temperature alternating environment.

8. The application according to claim 7, characterized in that, The aviation cable structure includes: an inner layer of copper conductor, a middle layer of fluorinated ethylene propylene copolymer or polytetrafluoroethylene insulation layer, and an outer layer of the high-toughness polyimide composite material sheath.

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